Diabolical process generating new compounds unknown to biology that they hoped human digestive tracts might metabolise. All in the name of long life cakes and grease for applying to bread prior to the jam.
.... and for years people went along with the food manufacturers and bought stuff adulterated with this foul mess.
P

Well, yes, but despite that it is on the AQA syllabus so I have to teach it. The lesson will mention the health implications, but I still need to teach what the syllabus calls 'Hardening' of a vegetable oil (far fewer giggles if they referred to it as hydrogenation).